Wood Beam Splice Over Column Detail

[JungleJoe]

Hi everyone, I was perusing Woodwork's library of details on their site and came across this one shown below. I'm considering the wisdom of the strap they show on the side of the beam. If the beam is spliced over the column then as the beams attempt to rotate won't the strap be in tension and cause splitting in the beam? My assumption is that the strap is there to provide a lateral connection from one beam to the other, but if a post-cap is installed as shown then is the strap needed? Or are the straps to prevent out-of-plane rotations between beams?

In any case, I've seen a similar detail where the strap is placed over the top of the beams instead of on the side, which seems better as far as the splitting issue is concerned. Woodworks is kind of the authority on wood construction so I hate to question their detail...

 

[XR250]

Woodworks is kind of the authority on wood construction so I hate to question their detail.

Are they? Did not know that.
I would only use the strap if the bolts could not resist the tension demand in the beam (if there is any)

 

[dik]

Why not a steel strap on top? I don't like using 'stacked' bolt connections because of possible splitting due to shrinkage.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[skeletron]

I haven't seen the strap with the post cap detail used in practice. It kind of seems geometrically a bit overkill as a CC66 would be 9.5" and the MSTC would be 3" wide, so it would need to be a 14" or 16" beam. I would avoid the strap over top if this were a PSL or similar beam because the nails would be into the narrow face.

The CWC shows a detail for deep beam over column that indicates bolts should be <12" from top of column, and if that can't work the detail indicates a cap with bolts at the shallow location and then an upper plate with bolts near the top of the beam. If I were concerned with out-of-plane rotations, that's the detail I would be drawn to instead of the strap. But I'd likely try some other framing arrangement if that were the case too...

 

[dik]

I'm not a wood guy, but I don't think PSL would be a problem... maybe LVL... and I really like using Glulam Rivets. With either of these, stacked bolts would not likely be an issue.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[skeletron]

@dik: Not a huge issue, but a 83% or 75% reduction for capacity if the nails are into the narrow face (over the top of beam as opposed to side face).
(sim.

https://www.bc.com/wp-content/uploa...Simpson-Connectors-Parallel-to-Gluelines.pdf)

 

[dik]

Thanks... for PSL (parallel strand lumber) material, or LVL (laminated veneer lumber) only?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[KootK]

In any case, I've seen a similar detail where the strap is placed over the top of the beams instead of on the side, which seems better as far as the splitting issue is concerned.

I don't understand the nature of your perceived splitting issue. Can you elaborate? I feel that the fasteners would either work for the tension demand by the numbers or they wouldn't -- end of story. In this respect, I don't see the tops side detail being much of an improvement other than for the fact that it increases the flexural lever arm on the connection a bit.

My assumption is that the strap is there to provide a lateral connection from one beam to the other, but if a post-cap is installed as shown then is the strap needed?

1) My first guess would have been a lateral tie connection too.

2) The post cap involves very few fasteners. The tension capacity of that connection could easily be overwhelmed by a serious chord / strut demand.

3) For this connection to be a viable, strong axis moment connection, one of these things would have to be true on the compression side of the beam:

a) The two member would have to be in direct, bearing contact and stay that way or;

b) The bolts in the post cap would have to be able to transfer the entire flexural compression force.

Both of those assumptions seem questionable to me. And this doesn't even get us into the question of whether or not axial slip in the tension fasters would neuter the beam continuity in its own right.

Or are the straps to prevent out-of-plane rotations between beams?

I doubt it. Again, fastener slip would probably neuter any perceived benefit.

 

[dik]

Maybe a problem with LVL material... I note the reductions in the link he posted.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[JungleJoe]

I've posted a couple of pics below that I found that sort of show what I'm thinking about. The first one is from Boise Cascade in their "Common Details" document. I'm probably thinking about this totally wrong but let's say you have a 20' wide deck where you have posts in the corners and then a midspan post at 10'.

1) Is it preferred to have a 20' long beam instead of two 10' long beams?
2) If, for one reason or another, you needed to go with two 10' long beams, would it be better to "pin" the connection rather than restraining rotation with the strap?

Most projects that I work on where this connection would come into play are on decks or long ridge beams with an interior support. I usually assume that a single, continuous beam is going to be used but in the case of splicing the beam at the support I'm wondering if I should always put a strap on there, even if I'm not anticipating any major chord forces into the beams (like on a deck where I try to move the shear into the back wall of the home).

 

[KootK]

The splitting that they show there is really the result of a tie connection not designed for the forces that it might see as a result of unintended beam continuity.

1) Is it preferred to have a 20' long beam instead of two 10' long beams?

Where handling and availability are not limitations, I do prefer continuous spans. Less deflection and more continuity.

2)If, for one reason or another, you needed to go with two 10' long beams, would it be better to "pin" the connection rather than restraining rotation with the strap?

Definitely, in my opinion.

Wood is kind of weird relative to other materials when it comes to providing rotational restraint at the supports. Quite often, there simply is not a mechanical connection that convincingly supplies that rotational restraint. I probably shouldn't say this out loud but I suspect that it works for wood because the proportions of the typical cross sections tend to give wood a degree of self stabilization rotationally. And there's nothing really analogous to the sidesway buckling that you might see with a steel wide flange beam. At extreme aspect ratios, I've no doubt that the self stabilization effect falls short.

 

[Harbringer]

In my neck of the woods strapping a wood beam line on the face of beam is a very normal detail to create a lateral drag. All of the perceived issues with the strap mentioned in this thread I've never observed. The beam will not rotate enough to overcome the nail slip in the strap. Woodworks detail is fine.

 

[JungleJoe]

Definitely, in my opinion.

Earlier you were talking about the benefits/need for the strap such as a chord force that overwhelms the post cap, but here I guess you're saying that you'd rather not have to have the strap at all if there won't be a tension force to resolve (which is basically what XR250 said earlier)?

Thanks everyone for your thoughts. No one is raising the alarm about the splitting (besides me lol), so for a beam splice over a support I can rest easy with a detail such as Woodwork's that has the strap on the side, even if tension in the beam is not anticipated.

 

[KootK]

Earlier you were talking about the benefits/need for the strap such as a chord force that overwhelms the post cap, but here I guess you're saying that you'd rather not have to have the strap at all if there won't be a tension force to resolve (which is basically what XR250 said earlier)?

Exactly. To the extent that there is a short coming in the Woodworks detail, I would say that it is in the title. Clearly, "continuous" is ambiguous. So is "beam splice". If the detail is meant to do what I think that it's meant to do then it would be spiffy to have that changed to, perhaps:

1) Indicate that the beam is not flexurally continuous.

2) Indicate that the beam is only spliced in so far as net axial load is concerned.

 

[phamENG]

So going down the road of tension only (which I agree with), it raises an interesting theoretical question:

In wood we don't mix fasteners - the slip characteristics are too variable to have bolts and nails work together in harmony. In that strap detail, you have to design the strap to take the full tension load. How many people consider the eccentricity it imposes on the beam and the resulting moment? Or do you just assume that the bolt carries enough to get rid of the eccentricity? I haven't run into this situation in a case where it made a difference, so I'm curious what others have done on a larger post and beam design.

OP - for the splitting, the concern is when the too much of section is trapped between a fastener group and bearing, or between two fastener groups that are in fixed relative positions. In this case, the post cap fasteners and the strap are separated, and can move vertically relative to one another. That allows the wood to shrink without building up stress at the fasteners and splitting.

 

[KootK]

In that strap detail, you have to design the strap to take the full tension load. How many people consider the eccentricity it imposes on the beam and the resulting moment? Or do you just assume that the bolt carries enough to get rid of the eccentricity?

Baring exceptional conditions, I normally would consider the tension eccentricity only conceptually. It's rare that I'd actually bother with numbers. Three reasons for that:

1) Bending + Tension is rather favorable when it comes to the various forms of buckling.

2) It takes a crap load of tension to produce a higher combined stress than the gravity load flexural stress usually.

3) It varies from case to case but, often, there actually is very little eccentricity between where the diaphragm delivers the axial load to the beam and where the strap ends up. It's rarely as bad as [T x h/2] etc.

Regardless, I wouldn't use the bolts to rectify the moment. Too much slop & slip in the bolt holes as you intimated.

 

[phamENG]

Thanks, KootK. That's more or less where my head was, though I hadn't really considered #3. Always nice to know what others are doing.